It is known from the state of the art to use a measuring tube for determining flow. A measuring transducer secured to the measuring tube or integrated into the measuring tube serves, in such case, to register a measured variable related to the flow through the measuring tube.
Known from the state of the art are different measuring principles for determining flow through such a measuring tube. Thus determining the flow can occur, for example, based on the ultrasonic measuring principle or based on the magneto inductive measuring principle.
Due to the different applications in which such flow measuring devices are applied, it is necessary to line the measuring tube with an electrically insulating material. This lining is selected as a function of the temperature and the measured material present in a particular application. Examples of materials include thermoplastic, thermosetting and elastomeric, synthetic materials.
Flow measuring devices are used by inserting them into pipelines. In such case, the measuring tube is connected at its two ends via flange connections with the adjoining pipeline sections. Known from the state of the art for sealing such flange connections are various kinds of seals. Thus, for example, Offenlegungsschrift (laid open German patent application DE 19846475 A1 discloses a flat sealing ring for establishing a flange connection. Further known from U.S. pat. No. US811,000 is a sealing ring, which serves for sealing a flange connection between two adjoining sections of a pipeline.
These known sealing surface geometries often require a high bearing pressure, in order to achieve adequate sealing. The high bearing pressure means, in turn, high bolt forces, which, lead to concentrated forces on the flanges. In order to keep flange warping small, the flanges must be correspondingly hefty, i.e. have a significant thickness.
Additionally, insertion of a sealing ring between two mutually adjoining pipeline sections provides the opportunity for gaps enabling escape of material at the joint.